Shunt Resistor Current Transformer Open Circuit Protection
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Solution Overview
Problem
Current transformers in electrical systems are prone to damage from open circuit failures in the control circuit, leading to high voltages across the secondary winding, which can result in insulation breakdown and require costly generator removal and repair in aircraft systems.
Innovation Solution
Incorporating a shunt resistor directly on the current transformer's secondary winding to maintain finite impedance and prevent insulation breakdown, even in the event of an open circuit fault, allowing continued operation without damaging the transformer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the control circuit or interconnection path experiences an open circuit failure, then the impedance across the secondary winding becomes infinite, but this causes extremely high voltages that break down insulation and render the current transformer inoperative
Solution Approach 1:
A shunt resistor is pre-connected across the secondary winding terminals before any open circuit failure occurs. This preliminary connection ensures that even if the control circuit opens, the shunt resistor remains in place to maintain a finite impedance path, preventing dangerous voltage buildup and protecting the insulation from breakdown.
Solution Approach 2:
The shunt resistor acts as an intermediary component between the secondary winding and the open control circuit. By providing an alternative current path with finite impedance, the shunt resistor mediates the harmful effect of the open circuit, preventing the transmission of extreme voltages to the insulation while allowing the current transformer to continue operating.
2Reliability
If a current transformer fails in an aircraft generator, then the generator must be removed from the aircraft for replacement, but this causes loss of aircraft operational time and increased maintenance costs
Solution Approach 1:
The shunt resistor is installed in advance on the current transformer, creating a protective measure that prevents catastrophic failure. This preliminary protection ensures that even if an open circuit occurs in the control system, the current transformer remains functional, eliminating the need for time-consuming generator removal and replacement operations.
Solution Approach 2:
The shunt resistor provides beforehand cushioning by absorbing the shock of open circuit failures. When the control circuit opens, the shunt resistor cushiones the resulting voltage spike, preventing insulation breakdown and allowing the current transformer to withstand the fault condition without damage, thus avoiding aircraft downtime.
3Measurement precision
If the voltage across the secondary winding is allowed to rise without limitation, then the control circuit can detect current imbalances, but this unlimited voltage rise can exceed insulation breakdown limits
Solution Approach 1:
The shunt resistor changes the impedance parameter of the secondary winding circuit from potentially infinite (open circuit) to a controlled finite value. This parameter change ensures that voltage remains within insulation breakdown limits while still allowing the control circuit to detect current imbalances through the shunt resistor's voltage output.
Solution Approach 2:
The shunt resistor serves as an intermediary that provides a controlled impedance path between the secondary winding and the open control circuit. It mediates between the need for voltage output (for imbalance detection) and the need to limit voltage (to protect insulation), converting the open circuit condition into a controlled voltage signal that preserves both measurement capability and insulation integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents insulation breakdown and allows continued operation of the electrical power system by maintaining finite impedance across the secondary winding, eliminating the need for generator removal and repair in case of open circuit failures.
Implementation Method 1
a resistor connected across the first and second ends
Data Source
AI summary
An electrical power system may comprise a power source, an electrical load and an interconnection path between the power source and the electrical load. At least one power-source current transformer may be positioned at the power source. At least one remote current transformer may be positioned remotely from the power-source current transformer so that a portion of the interconnection path is between the power-source and the remote current transformer. A control circuit may be interposed between the power-source and remote current transformers and may be responsive to current imbalance between the power-source and remote current transformers to disconnect the power source from the electrical load in the event of such imbalance. The at least one power-source current transformer may comprise a secondary winding having first and second ends, and a resistor connected across the first and second ends. This resistor may provide a path for current transformer secondary current to flow in the event of an open circuit failure in the control circuit or the interconnection path between the current transformer and the control circuit. Consequently voltage across the current transformer secondary may be limited to a level that will not damage the secondary windings. The control circuit may detect the open circuit failure and act to isolate the power source from the load with the minimum of time delay. The current transformer is thereby protected from open circuit failures.